Integrated wet lab and in silico discovery and characterization of bacteriophages with antibiotic synergy against multidrug resistant Acinetobacter baumannii

The global rise of multidrug-resistant (MDR) bacteria has rendered many conventional antibiotics ineffective, creating an urgent need for alternative therapeutic strategies. Among these, bacteriophage-based approaches offer targeted, self-amplifying antimicrobial activity with the potential to complement or restore antibiotic efficacy. We report the isolation, characterization and host-adaptation of phages from environmental samples using a set of standard experimental procedures. Using wastewater as the source, we isolated four Caudoviricetes phages infecting an MDR Acinetobacter baumannii clinical strain (Abau1). Genome sequencing and host‐prophage filtering identified two strictly lytic phages (ΦAb1-SL1 and ΦAb1-SL2) for characterization, whilst two phages were host-integrated. ΦAb1-SL1 demonstrated potent synergistic killing with cephalosporin antibiotics: checkerboard assays revealed strong synergy with cefiderocol, ceftazidime and cefotaxime, the first result confirmed by a time-killing assay. Conversely, no synergy was seen with carbapenems. Under our host‐adaptation protocol, ΦAb1-SL1 broadened its host-spectrum infecting a previously resistant A. baumannii strain (Abau2). The resulting adapted phage (ΦAb2-SL1) retained infectivity of both hosts, albeit at a lower titer on the new host. The observed phage–antibiotic synergy with cefiderocol underscores the therapeutic promise of combined phage–antibiotic regimens against MDR A. baumannii and highlights the efforts of a translational approach for assembling phage libraries.